1. Field of the Invention
The present invention relates to a fire alarm system which has a receiving section such as a fire receiver, and a transmitter for controlling, based on a control command from the receiving section, the monitoring of devices to be controlled such as zone bells, which devices are employed as terminal devices.
2. Description of the Related Art
In a conventional so-called R-type fire alarm system, coded signals are transmitted and received between a receiving section, such as a receiver, and terminal devices so as to perform fire monitoring and status maintenance. Terminal devices such as a fire detector and the like, employed in the fire alarm system, are controlled by a microprocessor. Such a microprocessor-controlled system requires that the types and addresses of the terminal devices be stored in a predetermined storage area of a memory. By utilizing the types and addresses stored in the memory, the fire receiver is able to specify a terminal device according to a call signal provided with a corresponding address so as to collect information on a change in the status of the specified terminal device and to transmit a control command to the specified terminal device.
For example, when a zone alarm transmitter for controlling, for example, the actuation of the zone bells, receives from the fire receiver an alarm command along with the designation of an address, it actuates the zone bells corresponding to the transmitter to sound.
However, the conventional alarm system of the above type encounters the following problems. A possible short circuit occurring in control lines for connecting the transmitter and the corresponding zone bells causes the fuse to melt and be broken. This inevitably requires the replacement of fuses afterwards, which is troublesome and complicated. Also, the actuating operation to sound the zone bells is performed uselessly when a short circuit has occurred in the control lines or when a wire break in power lines for connecting the fire receiver and the transmitter has occurred, resulting in unnecessary power consumption.
Moreover, whenever the fire receiver sends an alarm command to the transmitter, it always indicates that devices to be controlled, such as zone bells, are sounding. Hence, if any of signal lines between the fire receiver and the transmitter is faulty, or if a voltage fault occurs at power lines of the transmitter, the zone bells do not actually sound, but the fire receiver provides a false indication that the zone bells are sounding. Namely, since the transmitter, based on the actuating operation thereof, reliably returns a response signal to the fire receiver, the fire receiver provides a false indication that the zone bells are sounding, though it actually is not.
The respective problems suffered by the conventional system as discussed above are most likely to arise when another type of object device, such as a smoke exhausting device, is employed instead of the zone bell. The same applies to the use of another type of receiving section, such as a transmitter, in place of the fire receiver.